1. Field of the Invention
This invention relates to a clutch mechanism arranged to slippingly transmit rotation between a pair of rotating elements through a friction member such as felt or the like and also to a reel mount device which includes the clutch mechanism as a torque limiter for a video tape recorder, an audio tape recorder or the like.
2. Description of the Related Art
The recording and/or reproducing apparatuses of the kind using tapes as recording media, such as VTRs or the like, have heretofore been arranged to have built-in friction clutch mechanisms (frictional torque limiters) included in their reel mount devices which take up (send out) the tapes, with tape reels mounted thereon, for allowing the tapes to stably travel without being damaged.
The tape driving principle of an ordinary VTR is first described with reference to FIG. 5 as follows. The illustration includes a tape 1 which is a recording medium, a capstan 2, a pinch roller 3, a rotary drum 4 on which a head is mounted, a tension post 5, a take-up reel mount 6 (hereinafter referred to as a T reel mount), a supply reel mount 7 (hereinafter referred to as an S reel mount), a reel mount driving gear 8, an idler gear 9, a take-up side tape 1a which is wound around a take-up reel mounted on the T reel mount 6, and a supply side tape 1b which is wound around a supply reel on the S reel mount 7.
The tape 1 is pulled out from a cassette (not shown) to have a tape path formed in a recordable and/or reproducible state as shown in FIG. 5. In recording or reproducing, the tape 1 is pinched by the capstan 2 and the pinch roller 3 and caused to travel in the direction of arrow at a constant speed by controlling the rotation of the capstan 2. Signals are recorded or reproduced by the head of the rotary drum 4 on or from the traveling tape 1.
In this instance, a tension control mechanism which is not shown applies a back torque to the S reel mount 7, for example, through the tension post 5, a band brake wrapped around the S reel mount 7, a mechanical tension regulator, etc. The back torque is thus applied to effectively prevent the tape 1 from slackening.
The tape 1 sent out at a constant speed by the capstan 2 is taken up and wound by the T reel mount 6 through the reel mount driving gear 8 and an idler gear 9 which is driven by a reel motor. The winding rotational frequency required for the T reel mount 6 changes accordingly as the coil diameter of the take-up side tape 1a wound up by the T reel mount 6 changes. However, this change is absorbed and the winding torque is kept constant by a friction clutch mechanism which is disposed inside the T reel mount 6 in general. The T reel mount 6 is thus arranged to wind the tape 1 by rotating at a constant speed with slipping caused by the clutch mechanism as necessary.
The S reel mount 7 is arranged to act basically in the same manner as the T reel mount 6 when the tape 1 is caused to reversely travel in cases where the tape 1 is to be rewound through a friction clutch mechanism.
The friction clutch mechanism of the reel mount device is described next as follows. FIG. 6 is a sectional view of the T reel mount 6. FIG. 7 is an enlarged sectional view showing a part A shown in FIG. 6. The T reel mount 6 includes a reel mount gear 12 having a gear part formed along it periphery, a reel mount body 13, a reel engaging claw 14, a reel hub mounting face 15 which is located on the reel mount body 13 on the side of the tape, a felt member 16 employed as a friction member, a double-sided tape 17 employed as adhesion means, a thrust spring 18 employed as pressing contact means, a washer 19 and a sliding face 20 of the reel mount gear 12 which is arranged to be in slidable contact with the felt member 16.
The reel mount body 13 is rotatable. The reel mount gear 12 is rotatable coaxially with the reel mount body 13 and is urged in the direction of arrow B in FIG. 7 by the thrust spring 18 through the washer 19. The reel mount gear 12 is thus in a state of being pressed into contact with the felt member 16 which is secured to the reel mount body 13 by means of the double-sided tape 17. The reel engaging claw 14 of the reel mount body 13 is arranged to hold the tape reel hub with the reel hub mounting face 15 and to wind the tape by acting integrally with the reel mount body 13. The tape thus can be wound with the reel mount body 13 rotated by causing the reel mount gear 12 to rotate via the reel mount driving gear 8 at a predetermined rotational frequency while allowing the felt member 16 of the reel mount body 13 to slip over the sliding face 20 of the reel mount gear 12.
A slipping torque (a reel torque) obtained at this time is determined by a load of the thrust spring 18, the diameter of the felt member 16, a coefficient of friction between the felt member 16 and the sliding face 20 of the reel mount gear 12, etc.
There is a general demand for reduction in size of VTRs and particularly in size of camera-integrated type VTRs. To meet this demand, it has become desirous to arrange the mechanism of the reel mount device described above in a smaller size. As a result, the diameter of the felt member 16 tends to become smaller. Then, in order to obtain a desired torque, it has become necessary to increase the load of the thrust spring 18 accordingly.
However, in the case of the conventional device described above, the pressure sensitive adhesive of the double-sided tape 17 used for sticking the felt member 16 has sometimes come to seep under a high ambient temperature condition. In such a case, as shown in FIG. 8, the pressed contact force of the thrust spring 18 causes the pressure sensitive adhesive 21 to seep and spread around from the inner and outer peripheral edges 16a and 16b to the sliding face 20 of the reel mount gear 12. Then, as a result, some abnormality has taken place in frictional sliding between the felt member 16 and the sliding face 20. The abnormal frictional sliding has presented a problem in that it causes a higher reel torque and, in the worst case, brings about a rigidly connected state without slipping.
This problem has resulted from the reduction in diameter and thickness of the felt member 16 and, more particularly, from the trend of increasing the pressed contact force of the thrust spring 18 necessitated by the reduction in size of the reel mount device. This problem might throw impediments in applications of the reel mount device to a compact camera-integrated type VTR.